The invention relates to a fuel pump, and more particularly to a fuel pump that can modulate its speed to deliver the correct amount of fuel to satisfy demand.

Fuel pumps are used in aircraft for a number of purposes, such as transferring fuel from one tank to another. A principal use of fuel pumps is to supply fuel to the engines. Under normal conditions, a specific pump will supply fuel to one particular engine; however, each pump can supply fuel to more than one engine, to provide redundancy in the event of a pump failure. Further, the pump is often specified to supply fuel to more than one engine operating at maximum thrust (in case a pump fails during a period where maximum thrust is required).

Maximum thrust is normally only required during take-off and climb (a relatively small part of the flight). Further, pump failures are infrequent, and so a pump will spend a significant proportion (greater than 90%) of its operational life supplying fuel to a single engine operating at cruise.

Currently, fuel pumps are arranged to run at full capacity (supplying enough fuel for multiple engines at maximum thrust) all of the time, with excess fuel being returned to the tank. This mode of operation increases power consumption (as fuel that is not required by the engines is being pumped around the fuel system), and can reduce the life of the pump, requiring more frequent replacement.

According to a first aspect of the invention, there is provided a pump having a sensor for detecting output pressure of the pump and a controller for controlling a speed of the pump depending on the detected output pressure, wherein the controller is arranged to control the speed of the pump so as to maintain the output pressure at a desired level.

The output pressure may be sensed in any suitable manner. In a preferred form, the output pressure is sensed directly by a pressure sensor. Alternatively or additionally, the output pressure may be sensed indirectly by a flow rate sensor or similar. The pump may also include a sensor for detecting motor power of the pump. Correlating motor power and output pressure allows the efficiency of the pump to be determined, and this efficiency may be monitored so that degradation or wear of the pump can be detected.

The invention also extends to an aircraft having multiple engines and a pump as described above associated with each engine, wherein each pump is arranged to supply fuel to its associated engine, and is also arranged to supply fuel to another engine if the pump associated with that other engine fails.

With this arrangement, a single pump is arranged to supply a single engine under normal circumstance, but can also supply other engines if their pump fails. In the event of failure of a pump, its associate engine will seek fuel from another (still-working) pump, and the output pressure at the outlet of this pump will drop (as fuel is now being demanded by two engines rather than one). This drop in pressure can be sensed, and the controller can then increase the speed of the pump to maintain output pressure at a desired level, so that fuel can be supplied to both engines.

The invention also extends to a method of operating a pump, comprising the steps of:

sensing an output pressure of the pump; and controlling the speed of the pump so as to maintain the output pressure at a desired level.

A preferred embodiment of the invention will now be described by way of example only and with reference to the accompanying drawings in which:

Figure 1 is a schematic view of a prior art fuel pump arrangement; and

Figure 2 is a schematic view of a fuel pump arrangement according to the currently preferred embodiment.

As shown in Figure 1, a prior art fuel pump arrangement includes a fuel tank, a fuel pump connected to the fuel tank, and an engine (usually a jet engine) connected to the fuel pump. The fuel pump pumps fuel from the fuel tank to the jet engine. As mentioned above, the fuel pump as operated at a sufficient rate to pump enough fuel to for supply fuel to multiple engines operating at maximum thrust, to allow for pump failure during take-off. Flowever, the pump will normally only be supplying a single engine operating at cruise, which requires less fuel. Accordingly, the pump normally supplies more fuel than is needed, and the fuel which is not needed is returned through a fuel return line to the fuel tank. In the embodiment shown in Figure 2, the pump includes a sensor and a controller, which controls the output of the pump and allows the output of the pump to be varied. In the specific arrangement shown in Figure 2, a sensor (such as a pressure sensor or a flow rate sensor) is provided at or near the pump outlet, and supplies a signal corresponding to the sensed pressure or the sensed flow rate to a controller. The controller can determine the output pressure of the pump from this signal, and can in turn vary the pump motor speed depending on the received signal. The controller can be a microcontroller.

The pump senses the hydraulic load by monitoring the output pressure of the pump, whether directly, with a pressure sensor, or indirectly, by sensing the flow rate or some other parameter. It is also possible to provide both direct and indirect sensors, which allows a cross-check to be made on the detected pressure.

The pump normally supplies fuel sufficient for a single engine operating at cruise, and as fuel consumption for a single engine at cruise is quite steady, the output pressure of the pump will be relatively constant. However, if the engine demands more fuel for any reason, or if the pump is demanded to supply an additional engine as a result of failure of the pump which normally supplies that engine, the output pressure of the pump will fall. This drop in pressure will be detected by the sensor, and the controller can then modulate the motor speed (in this case, increase it) to maintain the output pressure.

Similarly, if the engine demands less fuel (for example, as the aircraft enters cruise after climbing), the output pressure of the pump will increase, and the controller can decrease motor speed to again maintain the output pressure.

Since the controller is a part of the pump, the pump is effectively self-controlling (or self- determining). Thus, there is no need for the pump to be controlled by the aircraft, and so no need for the pump to be connected to any pre-existing communication structure in the aircraft. This means that the pump is suitable to be used with a large number of aircraft.

In addition to the output pressure, further data can be gathered from the motor control system, such as motor power, speed, ambient temperature, and so on, to determine additional operating data points. The output pressure can be compared with motor power measurements to allow the efficiency of the pump to be monitored (although this may require additional

communication between the pump and the aircraft). Any change in efficiency can be detected and flagged as a potential issue, so degradation or wear of the pump can be detected quickly. It is also possible to monitor the health of the pump through frequency analysis of the pressure signal; for example, cavitation can be detected through frequency analysis in this way.

Controlling the pump in this way reduces the power consumption of the pump, as the pump is only supplying the amount of fuel that is required at any particular time. In an aircraft, all power consumed must eventually come from the fuel carried by the aircraft, and so reducing power consumption reduces the amount of fuel required. The applicant has estimated that for a typical wide-body application, making two eight-hour flights per day, the use of the pumps of the invention would save around 74 litres of fuel per day. This estimate does not include the amount of fuel required to carry the additional 74 litres, and so is conservative.

Although the pump has been described in the context of supplying fuel to the engines of an aircraft with multiple engines, it will be appreciated that the pump can be used in any situation where autonomous operation of a pump would be desirable.

In addition, the invention allows multiple physically identical pumps to supply different output pressures as required (for example, to allow preferential emptying of one fuel tank of an aircraft over another), by setting different output pressures of the pumps. This behaviour can be "programmed" when the pumps are installed, using for example a wire link in the connector, a software parameter loaded by a maintenance tool or a message received from the aircraft over a communications bus such as AFDX, CAN or the like.